Question

Which set of work should be used to solve the following problem?

How many moles are in 65.5 grams of PF3 gas? (molar mass of PF3=87.97 g/mol)




Group of answer choices

A. 65.5 g PF3 x (87.97 g PF3/1 mole)

B. 65.5 g PF3 x (1 gram PF3/87.97 mole)

C. 65.5 g PF3 x (1 mole/87.97 g PF3)

Answer 1

C. 65.5 g PF3 x (1 mole / 87.97 g PF3)

Step-by-step explanation:

Dimensional analysis can be used to find the amount of moles in 65.5 grams of PF3 gas.

First we would need to determine relevant conversions.

We would need to find the molar mass of PF3 which is already given ( 87.97 g / mol )

So 1 mole of PF3 = 87.97g

From there we can create the dimensional analysis table which will look something like the attached image.

This table correspond with answer choice C.

Reasons it's not the other answer choices.

It wouldn't be A because the units must cancel out and they don't as grams is being multiplied by grams

It would be B because it doesn't use correct units.

There are not 87.97 moles in 1 gram of PF3. There are 87.97 grams in 1 mole of PF3